What is a Regular Expression?
A regular expression (regex) is a sequence of characters that defines a search pattern. Regex is used extensively in software engineering for input validation, string parsing, data extraction, search-and-replace operations, and log analysis. Mastering regex is a critical skill for any developer working with text processing.
Real-Time Regex Testing
WhiteArray's Regex Tester lets you write a pattern and instantly see every match highlighted in your test string. Matches update as you type with zero delay, giving you immediate visual feedback on whether your pattern is correct. You can toggle regex flags like g (global), i (case-insensitive), m (multiline), and s (dotAll) with a single click.
Common Pattern Library
Don't want to write regex from scratch? We include a curated library of battle-tested patterns for common use cases: email validation, URL matching, IP addresses, phone numbers, dates, hex colours, and more. Click any preset to instantly load it into the editor and start testing against your own data.
100% Private & Client-Side
Your test strings and patterns are processed entirely in your browser. No data is ever transmitted to our servers. This makes it safe to test regex against production log data, API responses, or any sensitive text.